Sound concentrator



March 19, 1929. WQLVEKAM'P 1,706,018

,SOUND CONCENTRATOR Filed March 26, 1924 INVENTOR which Patented Mar.19, 1929.

UN'ITEDHSTA'TESF PATENT OFFICE.

MARI E. WOLVEKAMP, OI OAKLAND, CALIFORNIA.

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Application filed March 26, 1924. Serial No. 702,084.

termine the direction of an invisible soundsource.

Other objects and advantages will appear in the following specification,reference beinghad to the accompanying drawing, in

Figure 1 is a side elevation showing a sound-concentrator consisting intwo concave spherical reflectors in combination with the sound-conduitof a phonograph-recorder.-

Figure 2 is a side elevation showing a sound-concentrator consisting intwo concave spherical reflectors applied. to a telephone transmitter.

Figure 3 is a sectional View of a soundconcentrator consisting in twoconcave parabolic reflectors adapted for hearing of and determinin thedirection of distant sounds, showing also the double reflection of thesound-waves.

Figure .4 is a diagram of the sound-concentrator shown in Figure 2,illustrating the double reflection ofthe sonorous waves and the relativepositions of the principal and conjugate foci.

The underlying principle of this invention is to converge thesound-waves to a focus by means of a concave spherical or parabolicreflector and to throw back these concentrated sound-waves by means of asecond concave spherical or parabolic reflector through a hole at thepole or vertex in the first and larger reflector.

For the proper arrangement of the two sound-reflectors it is importantto know the exact positions of the foci and therefore I- preferreflectors of such a shape that their principal foci are in the planesand at the centers of their circular boundaries.

The diameters of the circular boundaries of such spherical or parabolicreflectors are therefore equal to respectively 2% and 4 times thedistance from the focus to the pole or vertex of the reflectors The mostpractical materials for these reflectors are metal, wood, ebonite; andlass.

InFigure 1 a spherical reflector 1 re ects the sound to a littlespherical reflector 2,

which is supported by bars 3 and reflects the, sound through a hole inreflector 1 leading inside the sound-conduit S C of aphonograph-recorder.

If a person sings before the large'reflector, the sonorous Waves will bereflected and at the same time converge for example to a point identicalwith the principal focus of the little reflector and hence parallelsound-waves will be thrown back through the hole at the pole of thelarge reflector. A little parabolic reflector may be substituted for thespherical reflector.

It is easy to see that such a sound-concentrator. will have a strongconcentrating power, dependent upon the diameters of the two reflectors.I I

Such a sound-concentrator is more effective than a horn of the same, or,as I found, of twice as large diameter.

Recent investigations by Foley and Cloud (The Physical Review, vol. 22,second series No. -1, p. 73) show that the so-called condensing power ofhorns having a large angle of flare may be partly imaginary.

J. H. Oloud showed that while a horn doubled the intensity of the soundemitted by an organ pipe, it acted merely as a resona: tor.

A, sound-concentrator not only is more effective than a'horn, but itdoes not distort the musical quality by resonanc In Figure 2the sphericareflector 4 re- 'flects the sound to the little spherical reflector 5,which is supported by bars 6 and throws the sound-waves back through themouthpiece M of a telephone transmitter T.

In Figure 3 a parabolic reflector reflects the sound-waves to a littleparabolic reflector,

which in turn reflects the sound-waves into the ear-tube and handle. Ifthe sound comes from a distant source, the parallel soundwaves will bereflected to the focus F, which in turn may be made the focus of thelittle reflector and hence parallel sound-waves will be sent through theear-tube H.

Such a sound concentrator is simple in arrangement and effective and mayalso be useful in determining the direction of invisible sound-sourcesas for example of ships in a fog or of airships and aeroplanes at night.

By moving the little parabolic reflector a little farther from thevertex V, convergent sound-Waves will be reflected through the eartube.

A better focussing may be obtained by using a little spherical reflectorinstead of the parabolic one.

In Figure 4, D and E denote opposite points on the circular boundary ofthe large reflector 4 with its principal focus F on the straight line DEand equidistant from the center of curvature U and the pole P.

For the little spherical reflector 5 the corresponding points are at d,e, f, c, and 19.

If the source of the sound 8 is nearby on the principal axis, thesound-Waves will be reflected to the conjugate focus 8 between 0 and F.

If s is situated between the center of ourvature c and the focus 7 ofthe little reflector, the sound-Waves Will converge to a point .X.

Following equations 2- of spherical aberration, althoughsuiiicientlyaccurate for all practical purposes.

The distances of the conjugate focus 8 to the principal foci F and f arein general very small.

If for example SP is equal to 10 FF and Zip to 7 fp, SF will be equal to1/9 FF and sf to 1/6 fp.

If X is at the center of the diaphragm of the transmitter, the strongesteffect will be obtained.

A similar sound-concentrator in combination With an ear-tube may bepractical for deaf people.

While the construction and arrangement of the sound-concentrators asherein described and claimed, is that of a generally preferred form,obviously modifications and changes can be made Without departing fromthe spirit of the invention or the scope of the claim.

I claim In a sound-concentrator, the combination of two open parabolicreflectors of distinctly different sizes, the concave surfaces of thesemainly empty reflectors being opposite to one another, the vertexand-principal focus of both reflectors being on the same principal axis,and vthe large reflector provided with a hole at its vertex for thepassage of the sound, substantially as set forth.

In testimony whereof I aflix my signature.

MARI E. WOLVEKAMP.

